Directed self-assembly process with size-restricted guiding patterns

ABSTRACT

A method includes providing a substrate; forming mandrel patterns over the substrate; and forming spacers on sidewalls of the mandrel patterns. The method further includes removing the mandrel patterns, thereby forming trenches that are at least partially surrounded by the spacers. The method further includes depositing a copolymer material in the trenches, wherein the copolymer material is directed self-assembling; and inducing microphase separation within the copolymer material, thereby defining a first constituent polymer surrounded by a second constituent polymer. The mandrel patterns have restricted sizes and a restricted configuration. The first constituent polymer includes cylinders arranged in a rectangular or square array.

PRIORITY

This application is a continuation of U.S. patent application Ser. No.15/197,467, entitled “Directed Self-Assembly Process withSize-Restricted Guiding Patterns,” filed Jun. 29, 2016, to Ming-HueiWeng et al., which claims the benefit of U.S. Prov. App. Ser. No.62/310,020, entitled “Directed Self-Assembly Process withSize-Restricted Guiding Patterns,” filed Mar. 18, 2016, each of which isherein incorporated by reference in its entirety.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experiencedexponential growth. Technological advances in IC materials and designhave produced generations of ICs where each generation has smaller andmore complex circuits than the previous generation. In the course of ICevolution, functional density (i.e., the number of interconnecteddevices per chip area) has generally increased while geometry size(i.e., the smallest component (or line) that can be created using afabrication process) has decreased. This scaling down process generallyprovides benefits by increasing production efficiency and loweringassociated costs. Such scaling down has also increased the complexity ofprocessing and manufacturing ICs.

For example, as optical lithography approaches its technological andeconomical limits, a directed self-assembly (DSA) process emerges as apotential candidate for patterning dense features such as contact holes.A DSA process takes advantage of the self-assembling properties ofmaterials, such as block copolymers, to reach nanoscale dimensions whilemeeting the constraints of current manufacturing. Typical DSA processesuse a guide pattern that “guides” the self-assembling process. Thegeometry of the guide pattern may affect the configuration of theself-assembled polymer features, as well as the final pattern density.Improvements in these areas are desired.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the dimensions of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIG. 1A shows a flow chart of a method of fabricating a semiconductordevice, according to various aspects of the present disclosure.

FIGS. 1B and 1C show flow charts of a method of fabricating asemiconductor device, according to an embodiment of the method of FIG.1A.

FIGS. 2A and 2B are top views of target mandrel patterns in the methodof FIG. 1A, in accordance with some embodiments.

FIGS. 2C, 2D, 2E, 2F, and 2G illustrate some configurations of DSAguiding patterns and nanodomains, according to aspects of the presentdisclosure.

FIGS. 3A, 3B, 3C, and 3D are cross sectional views of forming asemiconductor device according to the method of FIG. 1A, in accordancewith some embodiments.

FIGS. 3M and 3P are top views of forming a semiconductor deviceaccording to the method of FIG. 1A, in accordance with some embodiments.

FIGS. 3E-1, 3F-1, 3G-1, 3H-1, 3I-1, 3J-1, 3K-1, 3L-1, 3N-1, 3O-1, 3Q-1,3R-1, and 3S-1 are cross sectional views (along “1-1” lines in FIGS. 2A,2B, 3M, and 3P where applicable) of forming a semiconductor deviceaccording to the method of FIGS. 1A and 1B, in accordance with someembodiments.

FIGS. 3E-2, 3F-2, 3G-2, 3H-2, 3I-2, 3J-2, 3K-2, 3L-2, 3N-2, 3O-2, 3Q-2,3R-2, and 3S-2 are cross sectional views (along “2-2” lines in FIGS. 2A,2B, 3M, and 3P where applicable) of forming a semiconductor deviceaccording to the method of FIGS. 1A and 1B, in accordance with someembodiments.

FIGS. 4A, 4B, 4C, 4D, 4E, and 4F illustrate top views of forming asemiconductor device according to the method of FIG. 1A, in accordancewith some embodiments.

FIGS. 5A, 5B, 5C, 5D, and 5E illustrate top views of forming asemiconductor device according to the method of FIG. 1A, in accordancewith some embodiments.

FIGS. 6A, 6B, 6C, 6D, 6E, and 6F illustrate top views of forming asemiconductor device according to the method of FIG. 1A, in accordancewith some embodiments.

FIGS. 6G-1 and 6G-2 illustrate cross sectional views of forming asemiconductor device along “1-1” and “2-2” lines in FIG. 6F, accordingto the method of FIG. 1A, in accordance with some embodiments.

FIGS. 7A-1, 7A-2, 7B-1, 7B-2, 7C-1, 7C-2, 7D-1, 7D-2, 7E-1, 7E-2, 7F-1,and 7F-2 illustrate cross sectional views of forming a semiconductordevice according to the method of FIGS. 1A and 1C, in accordance withsome embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

The present disclosure is generally related to semiconductor devices,and more particularly to methods for manufacturing semiconductor devicesusing a DSA process. In a typical DSA process, a block copolymer (BCP)film having constituent polymers is formed over lithographically definedsurfaces, and a microphase separation is induced to cause theconstituent polymer molecules to self-assemble, thus creating denselypacked features with highly uniform dimensions and shapes. Typically, aguide pattern is created by a lithography process and the guide pattern“guides” the above DSA process. Some examples of the features that canbe created using DSA processes include cylindrical and lamellarnanodomains that are oriented perpendicular to a substrate. Thecylindrical nanodomains are found particularly promising for creatingdensely packed small contact holes for semiconductor devices. However, atypical BCP spontaneously forms hexagonal arrays of cylindricalnanodomains in a large area or a row of cylindrical nanodomains in anarrow trench. Either case does not suit the existing semiconductorfabrication very well because typical contact holes in a semiconductordevice are designed to be square-shaped. A rectangular or square arrayof cylindrical nanodomains will better suit existing semiconductordesign and fabrication. Accordingly, a goal of the present disclosure isto create cylindrical nanodomains that are arranged in a rectangular orsquare array. In an embodiment, the present disclosure achieves the goalby devising some novel guiding patterns for the DSA processes.

Referring now to FIG. 1A, a flow chart of a method 100 of forming asemiconductor device using a DSA process is illustrated according tovarious aspects of the present disclosure. The method 100 is merely anexample, and is not intended to limit the present disclosure beyond whatis explicitly recited in the claims. Additional operations can beprovided before, during, and after the method 100, and some operationsdescribed can be replaced, eliminated, or moved around for additionalembodiments of the method. An overview of the method 100 is brieflydescribed below in conjunction with FIGS. 2A-2G. It is followed by adetailed description of the method 100 in conjunction with FIGS. 3Athrough 3S-2 which are different views of a semiconductor structure 300according to various aspects of the present disclosure.

Referring to FIG. 1A, the method 100 receives a substrate at operation102, and forms mandrel patterns over the substrate at operation 104. Themandrel patterns have restricted sizes for constraining a subsequent DSAprocess. The method 100 may optionally remove some of the mandrelpatterns using a cut process at operation 106. Then it forms spacers onsidewalls of the mandrel patterns at operation 108. After removing themandrel patterns at operation 110 and treating the spacers at operation112, the method 100 performs a DSA process at operations 114 and 116using a BCP. The DSA process uses the treated spacers as guidingpatterns. The configuration of the spacers and the composition of theBCP result in desired constituent polymers (or nanodomains) arranged insquare or rectangular arrays. The method 100 may optionally remove someof the constituent polymers at operation 118 and transfer a patterncorresponding to one of the constituent polymers to the substrate. Inthe present embodiment, the desired constituent polymers arecylindrically shaped and are suitable for forming contact holes.

FIGS. 2A and 2B show top views of some examples of the mandrel patternsto be formed, constructed according to various aspects of the presentdisclosure. Referring to FIG. 2A, a target pattern 200 includes aplurality of mandrel patterns 202 arranged in a checkerboard-likeconfiguration. Unlike a typical checkerboard, the mandrel patterns 202are spaced apart. The mandrel patterns 202 can be divided into twogroups. A first group 200A of the mandrel patterns 202 is arranged in anarray with rows and columns (a 3×3 array in this example). A secondgroup 200B of the mandrel patterns 202 is arranged in another array withrows and columns (a 2×2 array in this example). Rows of the group (orarray) 200A are interleaved with rows of the group (or array) 200B, andcolumns of the group 200A are interleaved with columns of the group200B.

The mandrel patterns 202 are generally rectangular and are of about thesame size. In the example shown in FIG. 2A, each mandrel pattern 202 hasa dimension D_(x) along a direction “x” and a dimension D_(y) along adirection “y” perpendicular to the direction “x.” A mandrel pattern 202in the group 200A is spaced apart from an adjacent mandrel pattern 202in the group 200B by a spacing S_(x) along the direction “x” and aspacing S_(y) along the direction “y.” A pitch P_(x) of the mandrelpatterns 202 along the direction “x” is equal to twice of D_(x) plustwice of S_(x). A pitch P_(y) of the mandrel patterns 202 along thedirection “y” is equal to twice of D_(y) plus twice of S_(y). In thepresent embodiment, S_(x) is about equal to S_(y) which is a thicknessof the spacers to be formed on sidewalls of the mandrel patterns 202 atthe operation 108 (FIG. 1A). The mandrel patterns 202 are island-typemandrel patterns and the spacers are to be formed on outer sidewalls ofthe mandrel patterns 202.

Referring to FIG. 2B, a target pattern 210 includes a plurality ofmandrel patterns 212 that have about the same dimensions (D_(x) andD_(y)) and the same configuration (S_(x), S_(y), P_(x), and P_(y)) asthe mandrel patterns 202. One difference between the target patterns 200and 210 is that the mandrel patterns 212 are trench-type patterns andthe spacers are to be formed on inner sidewalls of the mandrel patterns212. Similar to the target pattern 200, the target pattern 210 can bedivided into two groups. A first group 210A of the mandrel patterns 212is arranged in an array with rows and columns (a 3×3 array in thisexample). A second group 210B of the mandrel patterns 212 is arranged inanother array with rows and columns (a 2×2 array in this example). Rowsof the group (or array) 210A are interleaved with rows of the group (orarray) 210B, and columns of the group 210A are interleaved with columnsof the group 210B.

FIGS. 2C-2G illustrate some exemplary configurations of guiding patterns222 and desired nanodomains 226 in the DSA process (operation 116). Theguiding patterns 222 are derived from the mandrel patterns 202 or 212.In the present embodiment, the guiding patterns 222 are spacers formedon sidewalls of the mandrel patterns 202 or 212. Therefore, the geometryof the mandrel patterns 202 or 212 controls the geometry of the guidingpatterns 222. The size of the nanodomains 226 is determined by thecomposition of the BCP in operation 116, such as the types and the ratioof constituent polymers in the BCP. In the present embodiment, thecomposition of the BCP and the surface property of the guiding patterns222 are tuned to produce cylindrical nanodomains 226 for contact holes.As shown in FIGS. 2C-2F, the geometry of the guiding patterns 222 aredesigned such that the nanodomains 226 form a rectangular or squarearray in each of the guiding patterns, and not a hexagonal array. Animmediate benefit is that the nanodomains 226 conform to existing ICdesign and fabrication flow.

Factors affecting the geometrical design of the guiding patterns 222include photolithography resolution in forming the mandrel patterns 202and 212, molecular weight of the BCP, and thermal stability of theconstituent polymers. For example, a smaller guiding pattern (having asmaller critical dimension) may demand a higher resolution in thephotolithograph processes. A larger guiding pattern may cause thenanodomains to form a hexagonal array because arranging in a hexagonalarray is more thermally stable than arranging in a square array. In thepresent embodiment, the geometry of the guiding patterns 222 is designedsuch that each array of nanodomains 226 has at most 4 rows and at most 4columns. In another word, the array may have a size (rows by columns orcolumns by rows) of 1 by 1, 1 by 2, 1 by 3, or 1 by 4 as shown in FIG.2C, or a size of 2 by 2, 2 by 3, or 2 by 4 as shown in FIG. 2D, or asize of 3 by 3 or 3 by 4 as shown in FIG. 2E, or a size of 4 by 4 asshown in FIG. 2F. Configurations shown in FIG. 2G may be produced byhaving an L-shaped guiding pattern 222 or by removing some of thenanodomains 226 from a rectangular or square array of nanodomains in oneof the FIGS. 2C-2F.

In below paragraphs, the method 100 is described in detail inconjunction with FIG. 3A through FIG. 3S-2 which are different views ofa semiconductor structure 300 according to various aspects of thepresent disclosure. The semiconductor structure 300 may be anintermediate device fabricated during processing of an IC, or a portionthereof, that may comprise static random access memory (SRAM) and/orother logic circuits, passive components such as resistors, capacitors,and inductors, and active components such as p-type FETs (PFETs), n-typeFETs (NFETs), FinFETs, metal-oxide semiconductor field effecttransistors (MOSFET), complementary metal-oxide semiconductor (CMOS)transistors, bipolar transistors, high voltage transistors, highfrequency transistors, other memory cells, and combinations thereof.

At operation 102, the method 100 (FIG. 1A) receives a substrate 302.Referring to FIG. 3A, the substrate 302 includes a material layer 304and a patterning target layer 306 where one or more patterns are to beformed therein. The material layer 304 includes one or more layers ofmaterial or composition. In some embodiments, the material layer 304includes an elementary semiconductor (e.g., silicon or germanium) and/ora compound semiconductor (e.g., silicon germanium, silicon carbide,gallium arsenic, indium arsenide, gallium nitride, and indiumphosphide). In some embodiments, the material layer 304 includes alloysemiconductors, such as silicon germanium carbide, gallium arsenicphosphide, and gallium indium phosphide. The material layer 304 may alsocomprise non-semiconductor materials including soda-lime glass, fusedsilica, fused quartz, calcium fluoride (CaF₂), and/or other suitablematerials. In some embodiments, the material layer 304 has one or morelayers defined within it, such as having an epitaxial layer overlying abulk semiconductor. In some embodiments, the material layer 304 includesa semiconductor-on-insulator (SOI) substrate. In an embodiment, thematerial layer 304 may include doped regions and have circuits formedthereon or therein.

The patterning target layer 306 is a hard mask layer in an embodiment.For example, it may include a dielectric material such as silicon oxideor silicon nitride. In another embodiment, the patterning target layer306 is an inter-layer dielectric (ILD) layer or an inter-metaldielectric (IMD) layer. For example, the patterning target layer 306 mayinclude a low-k or extreme low-k material. For example, the patterningtarget layer 306 may include materials such as tetraethylorthosilicate(TEOS) oxide, un-doped silicate glass, or doped silicon oxide such asborophosphosilicate glass (BPSG), fused silica glass (FSG),phosphosilicate glass (PSG), boron doped silicon glass (BSG), and/orother suitable dielectric materials. The patterning target layer 306 maybe formed over the material layer 304 through deposition or othermethods, such as physical vapor deposition (PVD), chemical vapordeposition (CVD) including plasma enhanced CVD (PECVD), and atomic layerdeposition (ALD).

At operation 104, the method 100 (FIG. 1) forms mandrel patterns (e.g.,the mandrel patterns 202 (FIG. 2A) or 212 (FIG. 2B)) over the patterningtarget layer 306. The mandrel patterns are to have restricted sizes asdiscussed above. This involves a variety of processes such asdeposition, photolithography, and etching, which are further describedbelow.

Referring to FIG. 3B, a hard mask (HM) layer 308 is deposited over thepatterning target layer 306. In some embodiments, the HM layer 308includes one or more dielectric materials, such as silicon oxide,silicon nitride, and/or silicon oxynitride (SiON). In some embodiments,the HM layer 308 includes titanium nitride (TiN). In some embodiments,the HM layer 308 has a thickness in a range from about 5 nm to about 50nm. In some embodiments, the HM layer 308 is formed using one or moreprocesses selected from the group consisting of CVD, PVD, ALD, spin-onmethods, sputtering, thermal oxidation, and a combination thereof.

In some embodiments, if the resolution of the photolithography equipmentpermits, the mandrel patterns 202 or 212 may be formed in the HM layer308 using one photolithography process. In the present embodiment, themethod 100 uses a double patterning method as shown in FIG. 1B toalleviate some of the requirements of the photolithography processes,such as optical wavelength and critical dimensions. Particularly, thedouble patterning method forms the group 200A (or 210A) using a firstphotolithography process and forms the group 200B (or 210B) using asecond photolithography.

Referring to FIG. 1B, at operation 132, the method 100 forms another HMlayer 310 over the HM layer 308 (FIG. 3C). The HM layer 310 may includea dielectric material, such as silicon oxide, silicon nitride, siliconoxynitride (SiON), or a low-k dielectric material; and may be formedusing one or more deposition processes aforementioned. The HM layer 310has different etch selectivity with respect to the HM layer 308.

The method 100 (FIG. 1B) forms the group 200A (or 200B) of the mandrelpatterns 202 (or 212) in the HM layer 310 using a process including afirst photolithography and one or more etching processes. Referring toFIG. 3D, a tri-layer stack is formed over the HM layer 310. Thetri-layer stack includes a bottom layer 312 over the HM layer 310, amiddle layer 314 over the bottom layer 312, and a photoresist (orresist) 316 over the middle layer 314. In some embodiments, the bottomlayer 312 and the middle layer 314 are optional, and the resist layer316 may be formed directly over the HM layer 310. In embodiments, thebottom layer 312 includes a bottom anti-reflection coating polymericmaterial, and the middle layer 314 includes silicon-containing polymer.In an embodiment, the resist 316 is a polymer sensitive to a radiationemployed by the first photolithograph. For example, the resist 316 maybe sensitive to an I-line light, a DUV light (e.g., 248 nm radiation bykrypton fluoride (KrF) excimer laser or 193 nm radiation by argonfluoride (ArF) excimer laser), a EUV light (e.g., 13.5 nm light), ane-beam, an x-ray, or an ion beam in some embodiments. The bottom layer312 and the middle layer 314 may be formed using deposition methodsdiscussed above, including spin-on coating. The resist 316 is spin-oncoated onto the middle layer 314 in the present embodiment.

Referring to FIGS. 3E-1 and 3E-2, the resist 316 is patterned to havethe geometries of the group 200A of the mandrel patterns 202 using thefirst photolithography process. In an embodiment, the firstphotolithography process includes exposing the resist 316 to a radiationsource using a mask having patterns corresponding to the group 200A,performing post-exposure bake processes, and developing the resist 316to remove portions thereof, which are either exposed or unexposedportions depending on the tone of the resist and the developing process.The developed resist 316 is also referred to as a resist pattern 316. Inanother embodiment, the first photolithography process may employ othertechnology, such as electron-beam direct writing without using a mask.

Referring to FIGS. 3F-1 and 3F-2, the HM layer 310 is etched to have thegeometries of the group 200A. This involves one or more etchingprocesses. For example, the middle layer 314 is etched through openingsof the resist pattern 316, the bottom layer 312 is etched throughopenings of the middle layer 314, and the HM layer 310 is etched throughopenings of the bottom layer 312. The resist pattern 316, the middlelayer 314, and the bottom layer 312 are removed, leaving the patternedHM layer 310 over the HM layer 308. The etching process for opening theHM layer 310 does not (or insignificantly) etch the HM layer 308. Thepatterned HM layer 310 forms a first plurality of mandrel patterns overthe HM layer 308, corresponding to the group 200A (or 210A) of themandrel patterns 202 (or 212).

The etching processes may use a dry (plasma) etching, a wet etching, orother suitable etching methods. For example, a dry etching process mayimplement an oxygen-containing gas, a fluorine-containing gas (e.g.,CF₄, SF₆, CH₂F₂, CHF₃, and/or C₂F₆), a chlorine-containing gas (e.g.,Cl₂, CHCl₃, CCl₄, and/or BCl₃), a bromine-containing gas (e.g., HBrand/or CHBR₃), an iodine-containing gas, other suitable gases and/orplasmas, and/or combinations thereof. For example, a wet etching processmay comprise etching in diluted hydrofluoric acid (DHF); potassiumhydroxide (KOH) solution; ammonia; a solution containing hydrofluoricacid (HF), nitric acid (HNO₃), and/or acetic acid (CH₃COOH); or othersuitable wet etchant. The resist pattern 316 may be removed using aplasma ashing process or a resist stripping process.

At operation 136, the method 100 (FIG. 1B) deposits another HM layer 318over the patterned hard mask layer 308 in preparation for a secondphotolithography process. Referring to FIGS. 3G-1 and 3G-2, the HM layer318 is formed over the HM layer 308 and covering the patterned HM layer310. The HM layer 318 may use a dielectric material such as siliconoxide, silicon nitride, silicon oxynitride (SiON), or a low-k dielectricmaterial. The HM layer 318 has different etch selectivity with respectto the HM layers 310 and 308.

At operation 138, the method 100 (FIG. 1B) patterns the HM layer 318 tohave the geometries of the group 200B (or 210B) of the mandrel patterns202 (or 212) by a process including a second photolithograph process.Referring to FIGS. 3H-1 and 3H-2, a resist pattern 320 is formed overthe HM layer 318. The resist pattern 320 may be formed by spin-coating aresist layer over the HM layer 318, exposing the resist layer to apattern corresponding to the group 200B (or 210B), performingpost-exposure bake processes, and developing the resist layer to formthe resist pattern 320. Referring to FIGS. 3I-1 and 3I-2, the HM layer318 is etched using the resist pattern 320 as an etch mask, therebyforming a second plurality of mandrel patterns over the HM layer 308,corresponding to the group 200B (or 210B). Referring to FIGS. 3J-1 and3J-2, the HM layer 308 is etched using both the patterned HM layer 310and the patterned HM layer 318 as an etch mask, thereby forming themandrel patterns 202 (or 212) in the HM layer 308. The etching processesfor the HM layers 318 and 308 may independently be a dry etching, a wetetching, or other suitable etching. The examples in FIGS. 3J-1 and 3J-2show island-type mandrel patterns 202. Similar fabrication process maybe used for forming trench-type mandrel patterns 212, for example, bydepositing a material layer over the patterned HM layer 308, planarizinga top surface of the material layer to expose the patterned HM layer308, and removing the patterned HM layer 308, thereby forming thetrench-type mandrel patterns 212 in the material layer.

At operation 106, the method 100 (FIG. 1A) may optionally perform a cutprocess to remove one or more of the mandrel patterns 202 (or 212). Inan embodiment, a cut process is another photolithography process thatforms a masking element over a portion of the mandrel patterns 202 (or212) and leaves another portion of the mandrel patterns 202 (or 212)exposed. Then, another etching process is performed to remove theexposed portion of the mandrel patterns 202, or a deposition process isperformed to fill in the exposed portion of the mandrel patterns 212. Afurther description of this cut process will be described in associationwith FIGS. 5A-5E later.

At operation 108, the method 100 (FIG. 1A) forms spacers 222 onsidewalls of the mandrel patterns 202 (or 212) which are in the form ofthe patterned HM layer 308. Referring to FIGS. 3K-1 and 3K-2, a spacerlayer 222 is deposited over the patterning target layer 306 and over thepatterned HM layer 308 as a blanket layer. The spacer layer 222 includesa nitride such as silicon nitride or titanium nitride in someembodiments and may be deposited using CVD, PVD, ALD, or other suitabledeposition methods. Referring to FIGS. 3L-1 and 3L-2, an anisotropic(dry) etching process is performed to remove portions of the spacerlayer 222 from the top surfaces of the patterning target layer 306 andthe patterned HM layer 308. Other portions of the spacer layer 222remain on the sidewalls of the mandrel patterns 308 and become thespacers 222. In the present embodiment, a thickness T_(x) of the spacers222 is about equal to the spacing S_(x) in FIGS. 2A and 2B.

At operation 110, the method 100 (FIG. 1A) removes the mandrel patterns202 (or 212), thereby forming trenches 223 that are at least partiallysurrounded by the spacers 222. FIG. 3M shows a top view of the spacers222 and the trenches 223, while FIGS. 3N-1 and 3N-2 show cross sectionalviews of the semiconductor device 300 along the “1-1” and “2-2” lines ofFIG. 3M, respectively. The trenches 223 have the dimensions thatgenerally match the dimensions of the mandrel patterns 202 in FIG. 2A(or the mandrel patterns 212 in FIG. 2B), taking into account dimensionvariations through the various photolithography and etching processesabove. The geometry of the trenches 223 conforms to the generalguideline discussed above, i.e., a rectangular or square array ofnanodomains 226 are to be formed inside each of the trenches 223 and thearray has at most 4 row and at most 4 columns. Further, some of thetrenches 223 are surrounded by the spacers 222 on all sides while someof the trenches 223 are only partially surrounded by the spacers 222.For example, trenches 223A, 223B, and 223C are fully surrounded by thespacers 222A, 222B, and 222C, respectively, while trench 223D issurrounded on three sides by the spacers 222A, 222B, and 222C. Stillfurther, the spacers 222 are connected to each other. For example, acorner of the spacer 222A joins a corner of the spacer 222B, and anothercorner of the spacer 222B joins a corner of the spacer 222C. The spacers222A and 222C are disposed on sidewalls of the mandrel patterns 202 (or212) formed using the first photolithography, while the spacer 222B isdisposed on sidewalls of the mandrel pattern 202 (or 212) formed usingthe second photolithography. In another example, a spacer 222D shares aside with the spacer 222B.

At operation 112, the method 100 (FIG. 1A) treats the surfaces of thespacers 222 and the patterning target layer 306. The operation 112 mayuse a plasma treatment or applying a surface modification material tothe spacers 222 and the patterning target layer 306 by a coating and/orrinsing process. The treatment makes the surfaces of the spacers 222 andthe patterning target layer 306 suitable for the subsequent DSA process,i.e., a BCP will be induced to form first and second constituentpolymers wherein the second constituent polymer surrounds the firstconstituent polymer and the first constituent polymer comprisesnanodomains oriented vertically to the substrate 302. For example, thetreatment may make the surfaces of the spacers 222 and the patterningtarget layer 306 more hydrophilic or hydrophobic, depending on the BCPto be used.

At operation 114, the method 100 (FIG. 1A) deposits a BCP 324 into thetrenches 223. Referring to FIGS. 3O-1 and 3O-2, in embodiments, the BCP324 is selected from the group consisting of poly(styrene-b-vinylpyridine), poly(styrene-b-butadiene), poly(styrene-b-isoprene),poly(styrene-b-methyl methacrylate), poly(styrene-b-alkenyl aromatics),poly(isoprene-b-ethylene oxide), poly(styrene-b-(ethylene-propylene)),poly(ethylene oxide-b-caprolactone), poly(butadiene-b-ethylene oxide),poly(styrene-b-t-butyl(meth)acrylate), poly(methylmethacrylate-b-t-butyl methacrylate), poly(ethylene oxide-b-propyleneoxide), poly(styrene-b-tetrahydrofuran), and combinations of theforegoing block copolymers. Further embodiments may also utilize acopolymer material 324 with a hydrophobic (or hydrophilic) firstconstituent and a hydrophilic (or hydrophobic) second constituent asthis facilitates segregation of the constituent polymers. The BCP 324 isdeposited with a coating or spin-on coating process in the presentembodiment.

At operation 116, the method 100 (FIG. 1A) induces microphase separationin the BCP 324 (i.e., constituent polymers in the BCP 324 segregate).FIG. 3P shows a top view of the semiconductor device 300, while FIGS.3Q-1 and 3Q-2 show cross sectional views of the semiconductor device 300along the “1-1” and “2-2” lines of FIG. 3P, respectively. Referring toFIG. 3P, in the present embodiment, the BCP 324 includes two constituentpolymers, a first constituent polymer (or first nanodomains) 226 and asecond constituent polymer (or second nanodomains) 228. The dimension,shape, and configuration of the first and second constituent polymers226 and 228 depend on various factors, such as the material used, therelative amounts of the constituent polymers, process variables such astemperature, the surface property of the spacers 222, among otherfactors. The spacers 222 act as the guiding pattern for microphaseseparation. An array of first constituent polymers 226 are formed withineach trench 223 (FIG. 3M). In the present embodiment, the array is a 1×2array (or a 2×1 array). Further, each of the first constituent polymers226 is a cylinder and is surrounded by the second constituent polymers228. Still further, the first and second constituent polymers 226 and228 are oriented vertically to the substrate 302. In variousembodiments, the inducing of the microphase separation may includeheating, cooling, introduction of a solvent, application of a magneticfield, and/or other techniques.

At operation 116, the method 100 (FIG. 1A) may optionally perform a cutprocess to remove one or more of the first and second constituentpolymers 226 and 228. In an embodiment, this cut process is anotherphotolithography process that forms a masking element over a portion ofthe first and second constituent polymers 226 and 228 and leaves anotherportion thereof exposed. Then, one or more deposition and/or etchingprocesses are performed to remove the exposed portion of the first andsecond constituent polymers 226 and 228 from the subsequentpattern-transfer process. A further description of this cut process willbe described in association with FIGS. 6A-6F later.

At operation 118, the method 100 (FIG. 1A) transfers a patterncorresponding to either the first constituent polymers 226 or the secondconstituent polymers 228 to the substrate 302. Referring to FIGS. 3R-1to 3S-2, in the present embodiment, a pattern corresponding to the firstconstituent polymers 226 is transferred to the patterning target layer306. Referring to FIGS. 3R-1 and 3R-2, the first constituent polymers226 is selectively removed by an etching process that does not etch orinsignificantly etches the spacers 222 and the second constituentpolymers 228, thereby forming openings 330. Referring to FIGS. 3S-1 and3S-2, the patterning target layer 306 is etched through the openings330, thereby transferring the pattern to the patterning target layer 306to have a plurality of trenches 332. The spacers 222 and the secondconstituent polymers 228 are removed thereafter. In an embodiment, thetrenches 332 are contact holes for forming contact features therein suchas source contacts, drain contacts, gate contacts, and vias connectingdifferent metal interconnect layers.

At operation 120, the method 100 (FIG. 1A) forms a final pattern ordevice. In an example, the method 100 forms contacts in the contactholes 332. For example, the method 100 may form a barrier layer onsidewalls of the contact holes 332 and subsequently fill in the contactholes 332 with a conductive material. The barrier layer may comprisetantalum (Ta), tantalum nitride (TaN), or another suitablemetal-diffusion barrier material; and may be deposited using CVD, PVD,ALD, or other suitable processes. The conductive material may usealuminum (Al), tungsten (W), copper (Cu), cobalt (Co), combinationsthereof, or other suitable material; and may be deposited using asuitable process, such as CVD, PVD, plating, and/or other suitableprocesses.

FIGS. 4A-4F illustrate the operations 104 through 116 of an embodimentof the method 100 (FIG. 1A) where the mandrel patterns are only partialarrays. Referring to FIG. 4A, a target pattern 400 includes mandrelpatterns 202 arranged in a seemingly irregular pattern. A group 400A ofthe mandrel patterns 202 forms a partial array, which is a subset of thearray 200A (FIG. 2A). A group 400B of the mandrel patterns 202 formsanother partial array, which is a subset of the array 200B (FIG. 2A).Rows of the group 400A interleaved with rows of the group 400B. Columnsof the group 400A interleaved with columns of the group 400B. Themandrel patterns 202 have restricted sizes, as discussed above withrespect to FIG. 2A. FIG. 4B shows another target pattern 410 whichincludes mandrel patterns 212. A group 410A of the mandrel patterns 212forms a partial array, while another group 410B of the mandrel patterns212 forms another partial array. The target patterns 400 and 410 aresimilar except that the mandrel patterns 202 are of island-type whilethe mandrel patterns 212 are of trench-type. The mandrel patterns 202and 212 may be formed over a substrate as discussed above with respectto operation 104. Referring to FIGS. 4C and 4D, spacers 222 are formedon sidewalls of the mandrel patterns 202 and 212 in a manner similar tooperation 108. Referring to FIG. 4E, the mandrel patterns are removed ina manner similar to operation 110, leaving trenches 223 surrounded bythe spacers 222 on at least three sides thereof. Referring to FIG. 4F,nanodomains 226 are formed in each of the trenches 223 in a rectangularor square array which has limited sizes as discussed above with respectto operations 112, 114, and 116.

The mandrel patterns shown in FIGS. 4A and 4B may be designed as such,or they may be derived from the mandrel patterns shown in FIGS. 2A and2B by using a cut process as discussed above with respect to operation106, which is further illustrated in FIGS. 5A-5E. Referring to FIG. 5A,mandrel patterns 202 are arranged in two arrays 200A and 200B that areinterleaved by rows and columns, as discussed above. Referring to FIG.5B, cut patterns 504 are implemented, in a separate photolithography inone example, to remove some of the mandrel patterns 202. In anembodiment, the cut process forms a masking element over the mandrelpatterns 202 and the masking element exposes the portion of the mandrelpatterns 202 overlapping with the cut pattern 504. Then a selectiveetching process removes this portion of the mandrel patterns 202.Referring to FIG. 5C, the remaining mandrel patterns 202 form partialarrays as discussed above with respect to FIG. 4A, and spacers 222 areformed on sidewalls of the mandrel patterns 202. Referring to FIG. 5D,the mandrel patterns 202 are removed to form trenches 223. Referring toFIG. 5E, nanodomains 226 are formed in each of the trenches 223 in arectangular or square array which has limited sizes.

FIGS. 6A-6F illustrate a cut process as discussed above with respect tooperation 118. FIG. 6A illustrates mandrel patterns 202 configured intwo interleaving arrays 200A and 200B. FIG. 6B illustrates spacers 222disposed on sidewalls of the mandrel patterns 202. FIG. 6C illustratestrenches 223 being surrounded by the spacers 222. FIG. 6D illustratesnanodomains 226 being formed using the spacers 222 as guiding patterns.Referring to FIG. 6E, cut patterns 630 are formed using aphotolithography process, removing a portion of the nanodomains 226.FIG. 6F illustrates the remaining nanodomains 226 for pattern-transferafter the cut process. In an embodiment, the cut patterns 630 areimplemented as a dielectric material filling the trenches 330 as shownin FIGS. 6G-1 and 6G-2 which are cross sectional views of thesemiconductor device 300 along the “1-1” and “2-2” lines of FIG. 6Frespectively.

FIG. 1C illustrates another embodiment of operation 104 according toaspects of the present disclosure. In this embodiment, operation 104includes the operation 132 for depositing a HM layer 310 over thesubstrate 302 and the operation 134 for forming a first array of mandrelpatterns in the HM layer 310 using a first photolithography. Furtheroperations of the operation 104 are briefly discussed below inconjunction with FIGS. 7A-1 through 7F-2 which are cross sectional viewsof the semiconductor device 300 along the “1-1” and “2-2” lines of FIG.2A respectively.

At operation 135, a buffer layer 340 is deposited over the substrate 302to cover the mandrel patterns 310 underneath and to provide a planar topsurface (FIGS. 7A-1 and 7A-2). In some embodiments, the buffer layer 340includes one or more polymers including silicon and may be formed usinga spin-on coating method and/or a suitable deposition method. Atoperation 137, trenches 344 are formed in the buffer layer 340.Referring to FIGS. 7B-1 and 7B-2, a resist pattern 342 is formed overthe buffer layer using a second photolithography process and providesthe trenches 344. Referring to FIGS. 7C-1 and 7C-2, the buffer layer 340is etched with the resist pattern 342 as an etch mask, thereby extendingthe trenches 344 into the buffer layer 340. At operation 136′, thetrenches 344 are filled with a dielectric HM material 346 as a secondarray of mandrel patterns (FIGS. 7D-1 and 7D-2). At operation 138′, thesemiconductor device 300 is planarized using a CMP process to expose themandrel patterns 310. Then, the buffer layer 340 is removed by anetching process, leaving the mandrel patterns 310 and 346 over the HMlayer 308 (FIGS. 7E-1 and 7E-2). Thereafter, the HM layer 308 is etchedwith the mandrel patterns 310 and 346 as an etch mask, forming themandrel patterns in the HM layer 308 (FIGS. 7F-1 and 7F-2).

Although not intended to be limiting, one or more embodiments of thepresent disclosure provide many benefits to a semiconductor device andthe formation thereof. For example, embodiments of the presentdisclosure provide guiding patterns and methods of forming the same fora DSA process. The guiding patterns have restricted sizes and restrictedconfiguration. The guiding patterns guide the DSA process to producecylindrical nanodomains arranged in a rectangular or square array. Suchconfiguration of nanodomains advantageously fits into existing IC designand fabrication flow, for example, in designing and forming contactholes.

In one exemplary aspect, the present disclosure is directed to a method.The method includes providing a substrate; forming mandrel patterns overthe substrate; and forming spacers on sidewalls of the mandrel patterns.The method further includes removing the mandrel patterns, therebyforming trenches that are at least partially surrounded by the spacers.The method further includes depositing a copolymer material in thetrenches, wherein the copolymer material is directed self-assembling;and inducing microphase separation within the copolymer material,thereby defining a first constituent polymer surrounded by a secondconstituent polymer.

In another exemplary aspect, the present disclosure is directed to amethod that includes providing a substrate; forming mandrel patternsover the substrate; forming spacers on sidewalls of the mandrelpatterns; and removing the mandrel patterns, thereby forming trenchesthat are at least partially surrounded by the spacers. The methodfurther includes depositing a copolymer material in the trenches,wherein the copolymer material is directed self-assembling; and inducingmicrophase separation within the copolymer material, thereby defining afirst constituent polymer surrounded by a second constituent polymer.The method further includes transferring a pattern corresponding toeither the first constituent polymer or the second constituent polymerto the substrate.

In another exemplary aspect, the present disclosure is directed to amethod that includes providing a substrate; forming a first array ofmandrel patterns over the substrate using a first photolithographyprocess; and forming a second array of mandrel patterns over thesubstrate using a second photolithography process. Rows of the firstarray and rows of the second array are interleaved, and columns of thefirst array and columns of the second array are also interleaved. Themethod further includes forming spacers on sidewalls of the mandrelpatterns; and removing the mandrel patterns, thereby forming trenchesthat are at least partially surrounded by the spacers. The methodfurther includes depositing a copolymer material in the trenches,wherein the copolymer material is directed self-assembling; and inducingmicrophase separation within the copolymer material, thereby defining afirst constituent polymer surrounded by a second constituent polymer.The method further includes transferring a pattern corresponding to thefirst constituent polymer to the substrate.

The foregoing outlines features of several embodiments so that those ofordinary skill in the art may better understand the aspects of thepresent disclosure. Those of ordinary skill in the art should appreciatethat they may readily use the present disclosure as a basis fordesigning or modifying other processes and structures for carrying outthe same purposes and/or achieving the same advantages of theembodiments introduced herein. Those of ordinary skill in the art shouldalso realize that such equivalent constructions do not depart from thespirit and scope of the present disclosure, and that they may makevarious changes, substitutions, and alterations herein without departingfrom the spirit and scope of the present disclosure.

What is claimed is:
 1. A method, comprising: providing a substratehaving spacers disposed thereupon, wherein the spacers define a trenchdisposed between the spacers; forming a directed self-assemblingcopolymer in the trench; and performing a microphase separation processon the directed self-assembling copolymer to form a first constituentpolymer in the trench and a second constituent polymer in the trenchdisposed between the first constituent polymer and the spacers, suchthat the second constituent polymer fully surrounds the firstconstituent polymer from a top view.
 2. The method of claim 1 furthercomprising: selectively removing the first constituent polymer such thatthe second constituent polymer and the spacers remain.
 3. The method ofclaim 2 further comprising: performing a fabrication process on aportion of the substrate exposed by the removing of the firstconstituent polymer.
 4. The method of claim 3, wherein the fabricationprocess includes etching the portion of the substrate exposed by theremoving of the first constituent polymer.
 5. The method of claim 1,wherein the providing of the substrate having the spacers includes:forming a mandrel on the substrate; forming the spacers on side surfacesof the mandrel; and removing the mandrel such that the spacers remain.6. The method of claim 1, wherein the microphase separation processforms a plurality of regions of the first constituent polymer betweenthe spacers and separated by the second constituent polymer.
 7. Themethod of claim 6, wherein each of the plurality of regions of the firstconstituent polymer is cylindrical.
 8. The method of claim 1, wherein:the trench is a first trench; the spacers further define a second trenchdisposed between the spacers; the directed self-assembling copolymer isfurther formed in the second trench; and the performing of themicrophase separation process forms the first constituent polymer andthe second constituent polymer in the second trench.
 9. A method,comprising: providing a substrate; forming a patterned hard mask on thesubstrate; forming spacers on sidewalls of the patterned hard mask;removing the patterned hard mask such that the spacers define aplurality of trenches bounded by the spacers and the substrate, forminga copolymer material in the trenches; inducing microphase separationwithin the copolymer material, thereby defining, in a first trench ofthe trenches, a first cylindrical-shaped constituent polymer and asecond constituent polymer that wraps around the firstcylindrical-shaped constituent polymer and is disposed between the firstcylindrical-shaped constituent polymer and the spacers; and transferringa pattern corresponding to either the first constituent polymer or thesecond constituent polymer to the substrate.
 10. The method of claim 9,wherein the first cylindrical-shaped constituent polymer and the secondconstituent polymer have different etching sensitivities.
 11. The methodof claim 9, wherein the transferring of the pattern includes removingthe first cylindrical-shaped constituent polymer such that the secondconstituent polymer and the spacers remain.
 12. The method of claim 9,wherein the transferring of the pattern includes etching an exposedportion of the substrate.
 13. The method of claim 9, wherein themicrophase separation forms a plurality of regions of the firstconstituent cylindrical-shaped polymer between the spacers that areseparated by the second constituent polymer.
 14. The method of claim 13,wherein each of the plurality of regions of the first cylindrical-shapedconstituent polymer is vertically oriented to the substrate.
 15. Amethod, comprising: providing a substrate; forming an array of mandrelpatterns over the substrate; forming spacers on sidewalls of eachmandrel of the array of mandrel patterns; removing the array of mandrelpatterns, thereby defining trenches between the spacers; depositing acopolymer material in the trenches; inducing microphase separationwithin the copolymer material, thereby defining a first constituentpolymer laterally and concentrically surrounded by a second constituentpolymer within each of the trenches; and transferring a patterncorresponding to the first constituent polymer to the substrate.
 16. Themethod of claim 15, wherein the transferring of the pattern includesselectively removing the first constituent polymer.
 17. The method ofclaim 15, wherein the transferring of the pattern includes etching aportion of the substrate exposed by the second constituent polymer andthe spacers.
 18. The method of claim 1, wherein the directedself-assembling copolymer is selected from the group consisting ofpoly(styrene-b-vinyl pyridine), poly(styrene-b-butadiene),poly(styrene-b-isoprene), poly(styrene-b-methyl methacrylate),poly(styrene-b-alkenyl aromatics), poly(isoprene-b-ethylene oxide),poly(styrene-b-(ethylene-propylene)), poly(ethyleneoxide-b-caprolactone), poly(butadiene-b-ethylene oxide),poly(styrene-b-t-butyl(meth)acrylate), poly(methylmethacrylate-b-t-butyl methacrylate), poly(ethylene oxide-b-propyleneoxide), poly(styrene-b-tetrahydrofuran), and combinations thereof. 19.The method of claim 1, wherein the first constituent polymer and thesecond constituent polymer have different etching sensitivities.
 20. Themethod of claim 15, wherein the first constituent polymer is cylindricalin a top-down view.